Transcript Section 27.2 Summary – pages 728-733

Annelida
Segmented Worms
N0- not that kind of worm!
Common Examples
• Earthworms
Common Examples
• Bristle Worms
Common Examples
• Feather Duster Worms
Common Examples
• Tube Worms
Common Examples
• Tube Worms
Common Examples
• Leeches
• Rag Worm
How
would
you like
to run
into the
jaws of
this guy!
Characteristics
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Segmentation
Cephalization
Bilateral Symmetry
Coelomates
One way digestive tract
Both Filter Feeders and Predators
Asexual and Sexual Reproduction
Water and Land Examples
Segmentation
•Each segment repeats
•Very efficient design.
•Some are specialized
•Digestion, reproduction,excretion,
etc.
Definite Head End
Annelida has
Bilateral Symmetry
Yes,
Symmetric
No, not
Symmetric
No, not
Symmetric
Body Structure
• The basic body plan = a tube within a tube
• internal tube=
suspended w/in
coelom = digestive
tract.
Phylum Annelida
• Hydrostatic skeleton
–
–
–
–
Fluid pressure in coelom provides support & locomotion
Circular muscles
Longitudinal muscles
Peristaltic locomotion – squeeze, relax, squeeze!
Body Structure
• SETAE = tiny
bristles on each
segment
• help move
• anchors body in
soil so each
segment can move
the animal along
Setae
Phylum Annelida
• Setae (“bristles”) of chitin – a carbohydrate
• Chitin forms the exoskeleton in insects, shrimp, crayfish, etc.
– “anchors” for earthworm
– “paddles” for polychaete
– Enlarged as jaws in leeches, some polychaetes
Body Structure
• distinguishing characteristic is that bodies are
divided into ringed segments
• In most species,
segmentation
continues
internally as each
segment is
separated from the
others by a body
partition.
Segments
Body Structure
• Each segment has its own muscles, allowing
shortening and lengthening of the body.
• Segmentation also allows for specialization
of body tissues.
• Certain segments have modifications for
functions such as sensing and reproduction.
Nervous system
• Segmented worms have simple nervous
systems in which organs in anterior segments
have become modified for sensing the
environment = cephalization
• Some sensory organs are sensitive to light,
and eyes with lenses and retinas have
evolved in certain species.
Nervous system
• In some species
there is a brain
located in an
anterior segment.
• Nerve cords
connect the brain
to nerve centers
called ganglia,
located in each
segment.
Setae
Brain
Phylum Annelida
• Closed circulatory system
– Multiple “hearts”
– Hemoglobin not in
blood cells
• reddish-pink color
• Blood carries O2 to and
CO2 from body cells
• flow through vessels to
reach all parts of the body
• must live in water or in
wet areas on land because
they exchange gases
directly through their
moist skin – like your
lungs
Digestion and Excretion
• complete internal digestive tract
• length of body
• Nutrients diffuse to blood
• Transported to all cells
• Food > mouth > crop >gizzard > gut >anus
Digestion and Excretion
Crop
• GIZZARD
• a muscular
sac
• Contains hard
particles to
grind soil and
food before
they pass into
intestine/gut
Mouth
Circulatory
System
Gizzard
Excretion
• have two nephridia in
almost every segment.
• Special cells that collect
waste and transport it
through the coelom and
out of the body.
Nephridia
Reproduction
• Earthworms and leeches are hermaphroditic
– exchange sperm.
• forms a capsule for the eggs and sperm.
• The eggs fertilized in capsule, then it slips off the worm and
left in soil
• 2-3 weeks, young worms emerge from the eggs.
Reproduction in Bristleworms
• separate sexes and reproduce sexually.
• eggs and sperm are released into seawater and fertilize there
= external fertilizaton
• larvae hatch in sea
• become part of the plankton –important part of food chain
• Eventually settles to the bottom to live
CLASSES OF ANNELIDA
• ClassOligochaeta - earthworms
• Class Polychaeta - bristleworms
• Class Hirudinea - leeches
Class Oligochaeta: Earthworms
• most well-known annelids
• Easily seen by most people.
• burrows through soil
• Loosens and aerates soil
• Feces = “castings” = fertilizer
• Ecologically very important
• Possible human food source= protein
Class Polychaeta: Bristleworms
• Polychaete
means “many
bristles”
• Most body
segments have
many setae
• has a head with well-developed sense organs,
including eyes.
Class Polychaeta: Bristleworms
• have parapodia,
(paired feet)
• can be used for
swimming or
crawling over
corals and bottom
of sea.
• Parapodia also function in gas exchange.
Class Hirudinea: Leeches
• segmented worms with flattened bodies
• usually no setae
• Many are
parasites
• suck blood or
other body fluids
from hosts
(ducks, turtles,
fish, and
humans).
Hirudinea: Leeches
• Front and rear suckers for attachment
• saliva contains:
– anesthetic chemicals
– Anticoagulants – prevent clotting of blood
• can ingest 2 to 5 times its weight in 1 meal.
Origins of Segmented Worms
• Annelids probably evolved in the sea,
perhaps from larvae of ancestral flatworms.
•Tubes constructed
by polychaetes are
the most common
fossils of this
phylum.
•Some of these tubes
appear in the fossil
record as early as
540 million years
ago.